U.S. patent application number 13/874920 was filed with the patent office on 2014-04-03 for normally-off high electron mobility transistor.
This patent application is currently assigned to Samsung Electronics Co., Ltd.. The applicant listed for this patent is SAMSUNG ELECTRONICS CO., LTD.. Invention is credited to Sun-kyu HWANG, Woo-chul JEON, Joon-yong KIM, Kyoung-yeon KIM, Jae-joon OH, Ki-yeol PARK, Young-hwan PARK, Jai-kwang SHIN.
Application Number | 20140091363 13/874920 |
Document ID | / |
Family ID | 48656003 |
Filed Date | 2014-04-03 |
United States Patent
Application |
20140091363 |
Kind Code |
A1 |
JEON; Woo-chul ; et
al. |
April 3, 2014 |
NORMALLY-OFF HIGH ELECTRON MOBILITY TRANSISTOR
Abstract
According to example embodiments, a normally-off high electron
mobility transistor (HEMT) includes: a channel layer having a first
nitride semiconductor, a channel supply layer on the channel layer,
a source electrode and a drain electrode at sides of the channel
supply layer, a depletion-forming layer on the channel supply
layer, a gate insulating layer on the depletion-forming layer, and
a gate electrode on the gate insulation layer. The channel supply
layer includes a second nitride semiconductor and is configured to
induce a two-dimensional electron gas (2DEG) in the channel layer.
The depletion-forming layer is configured has at least two
thicknesses and is configured to form a depletion region in at
least a partial region of the 2DEG. The gate electrode contacts the
depletion-forming layer.
Inventors: |
JEON; Woo-chul; (Daegu,
KR) ; PARK; Young-hwan; (Seoul, KR) ; OH;
Jae-joon; (Seongnam-si, KR) ; KIM; Kyoung-yeon;
(Seongnam-si, KR) ; KIM; Joon-yong; (Seoul,
KR) ; PARK; Ki-yeol; (Suwon-si, KR) ; SHIN;
Jai-kwang; (Anyang-si, KR) ; HWANG; Sun-kyu;
(Seoul, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SAMSUNG ELECTRONICS CO., LTD. |
Suwon-Si |
|
KR |
|
|
Assignee: |
Samsung Electronics Co.,
Ltd.
Suwon-Si
KR
|
Family ID: |
48656003 |
Appl. No.: |
13/874920 |
Filed: |
May 1, 2013 |
Current U.S.
Class: |
257/194 |
Current CPC
Class: |
H01L 29/402 20130101;
H01L 29/7786 20130101; H01L 29/2003 20130101; H01L 29/1066
20130101; H01L 29/778 20130101; H01L 29/42316 20130101 |
Class at
Publication: |
257/194 |
International
Class: |
H01L 29/778 20060101
H01L029/778 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 28, 2012 |
KR |
10-2012-0109267 |
Claims
1. A normally-off high electron mobility transistor (HEMT)
comprising: a channel layer including a first nitride
semiconductor; a channel supply layer on the channel layer, the
channel supply layer including a second nitride semiconductor, the
channel supply layer configured to induce a two-dimensional
electron gas (2DEG) in the channel layer; a source electrode and a
drain electrode at sides of the channel supply layer; a
depletion-forming layer on the channel supply layer, the
depletion-forming layer configured to form a depletion region in at
least a partial region of the 2DEG, the depletion-forming layer
having at least two thicknesses; a gate insulation layer on the
depletion-forming layer; and a gate electrode on the gate
insulation layer, the gate electrode contacting the
depletion-forming layer.
2. The normally-off HEMT of claim 1, wherein the depletion-forming
layer includes a first part having a first thickness, and the
depletion-forming layer includes a second part at a side of the
first part and, the depletion-forming layer includes a third part
at a different side of the first part, the second part and the
third part having a second thicknesses.
3. The normally-off HEMT of claim 2, wherein the first thickness is
thicker than the second thickness.
4. The normally-off HEMT of claim 2, wherein the first part of the
depletion-forming layer is a strip shape, the second part and the
third part of the depletion-forming layer are a strip shape in
parallel to the first part.
5. The normally-off HEMT of claim 2, wherein the second part and
the third part are spaced apart from the source electrode and the
drain electrode, respectively.
6. The normally-off HEMT of claim 5, wherein the first part of the
depletion-forming layer is configured to form the depletion region
below the first part, and an electron density of the 2DEG below the
at least one of the second part and the third part of the
depletion-forming layer is relatively lower than an electron
density of the 2DEG that is not located below the depletion-forming
layer.
7. The normally-off HEMT of claim 2, wherein at least one of the
second part and the third part of the depletion-forming layer
contacts a corresponding one of the source electrode and the drain
electrode.
8. The normally-off HEMT of claim 2, wherein the gate electrode is
on the gate insulation layer above at least a portion of the first
to third parts of the depletion-forming layer.
9. The normally-off HEMT of claim 2, wherein the gate insulating
layer defines an opening that exposes a portion of the
depletion-forming layer, and the gate electrode contacts the
depletion-forming layer through the opening.
10. The normally-off HEMT of claim 9, wherein the opening in the
gate insulating layer is on the first part of the depletion-forming
layer.
11. The normally-off HEMT of claim 2, further comprising: a first
gate electrode formed between the first part and the gate
insulation layer, wherein the first gate electrode and the gate
electrode are electrically connected to each other.
12. The normally-off HEMT of claim 11, further comprising: a wire
that electrically connects the first gate electrode and the gate
electrode, wherein the gate insulation layer exposes the first gate
electrode.
13. The normally-off HEMT of claim 11, wherein the gate insulation
layer defines an opening that exposes the first gate electrode, and
the first gate electrode and the gate electrode are electrically
connected to each other through the opening.
14. The normally-off HEMT of claim 1, wherein the first nitride
semiconductor includes a gallium nitride (GaN) group material.
15. The normally-off HEMT of claim 1, wherein the second nitride
semiconductor includes a nitride including at least one of aluminum
(Al), gallium (Ga), indium (In) and boron (B).
16. The normally-off HEMT of claim 1, wherein the depletion-forming
layer includes a p-type nitride semiconductor.
17. The normally-off HEMT of claim 16, wherein the
depletion-forming layer includes a group III-V nitride
semiconductor material.
18. The normally-off HEMT of claim 1, wherein the depletion-forming
layer includes a first part having a first thickness, the
depletion-forming layer includes a second part having a second
thickness that is different than the first thickness, the first
part of the depletion-forming layer separates the gate electrode
and the channel supply layer by a greater distance than the second
part of the depletion-forming layer separates the gate electrode
and the channel supply layer.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority under 35 U.S.C. .sctn.119
to Korean Patent Application No. 10-2012-0109267, filed on Sep. 28,
2012, in the Korean Intellectual Property Office, the disclosure of
which is incorporated herein in its entirety by reference.
BACKGROUND
[0002] 1. Field
[0003] Example embodiments relate to a normally-off high electron
mobility transistor (HEMT), and more particularly, to a
normally-off HEMT including a depletion-forming layer.
[0004] 2. Description of the Related Art
[0005] Various power conversion systems may include a device for
controlling a current flow by ON/OFF switching thereof, e.g., a
power device. The efficiency of a power conversion system may
depend on the efficiency of a power device in the power conversion
system.
[0006] Many power devices commercialized at present are silicon
(Si)-based power Metal-Oxide-Semiconductor Field-Effect Transistors
(MOSFETs) and Insulated Gate Bipolar Transistors (IGBTs). However,
increasing the efficiency of a silicon-based power device may be
limited by the physical properties of silicon, manufacturing
processes, and so forth. To overcome these limitations, research
has looked at using a group III-V compound semiconductor in a power
device. In association with this, a high electron mobility
transistor (HEMT) using a heterojunction structure of a compound
semiconductor has attracted attention.
[0007] A HEMT may include semiconductor layers having different
electrical polarization characteristics. In a HEMT, a semiconductor
layer having a relatively high polarization rate may induce a
two-dimensional electron gas (2DEG) in another semiconductor layer
attached thereto, and the 2DEG may have very high electron
mobility.
[0008] When a gate voltage of a HEMT is 0 V, power consumption may
occur in a normally-on state in which a current flows between drain
and source electrodes thereof due to a low resistance therebetween.
To change to a normally-off state in which no current flows between
the drain and source electrodes, a negative voltage may be applied
to a gate electrode of a HEMT.
[0009] As another method, a HEMT having a depletion-forming layer
to implement a normally-off characteristic by which no current
flows between drain and source electrodes of the HEMT when a gate
voltage thereof is 0 V has been researched.
SUMMARY
[0010] Example embodiments relate to a normally-off high electron
mobility transistor (HEMT) using a depletion-forming layer.
[0011] Additional aspects will be set forth in part in the
description which follows and, in part, will be apparent from the
description, or may be learned by practice of example
embodiments.
[0012] According to example embodiments, a normally-off high
electron mobility transistor (HEMT) includes: a channel layer
including a first nitride semiconductor; a channel supply layer on
the channel layer, the channel supply layer including a second
nitride semiconductor, the channel supply layer configured to
induce a two-dimensional electron gas (2DEG) in the channel layer;
a source electrode and a drain electrode at sides of the channel
supply layer; a depletion-forming layer on the channel supply
layer, the depletion-forming layer configured to form a depletion
region in at least a partial region of the 2DEG, the
depletion-forming layer having at least two thicknesses; a gate
insulation layer on the depletion-forming layer; and a gate
electrode on the gate insulation layer, the gate electrode
contacting the depletion-forming layer.
[0013] In example embodiments, the depletion-forming layer may
include a first part having a first thickness, a second part at a
side of the first part, and a third part at a different side of the
first part. The second part and the third part may have a second
thickness.
[0014] In example embodiments, the first thickness may be thicker
than the second thickness.
[0015] In example embodiments, the first part of the
depletion-forming layer may be a strip shape, and the second part
and third part may be a strip shape in parallel to the first
part.
[0016] In example embodiments, the second part and the third part
may be spaced apart from the source electrode and the drain
electrode, respectively.
[0017] In example embodiments, the first part of the
depletion-forming layer may be configured to form the depletion
region below the first part, and an electron density of the 2DEG
below the second part and the third part of the depletion-forming
layer may be lower than an electron density of the 2DEG that is not
located below the depletion-forming layer.
[0018] In example embodiments, at least one of the second part and
the third part of the depletion-forming layer may contact a
corresponding one of the source electrode and the drain
electrode.
[0019] In example embodiments, the gate electrode may be on the
gate insulation layer above at least a portion of the first to
third parts of the depletion-forming layer.
[0020] In example embodiments, the gate insulating layer may define
an opening that exposes a portion of the depletion-forming layer,
and the gate electrode may contact the depletion-forming layer
through the opening.
[0021] In example embodiments, the opening may be on the first part
of the depletion-forming layer.
[0022] In example embodiments, the normally-off HEMT may further
include a first gate electrode between the first part and the gate
insulation layer, wherein the first gate electrode and the gate
electrode may be electrically connected to each other.
[0023] In example embodiments, the normally-off HEMT may further
include a wire that electrically connects the first gate electrode
and the gate electrode, and the gate insulation layer may expose
the first gate electrode.
[0024] In example embodiments, the gate insulation layer may define
an opening that exposes the first gate electrode, and the first
gate electrode and the gate electrode may be electrically connected
to each other through the opening.
[0025] In example embodiments, the first nitride semiconductor may
include a gallium nitride (GaN) group material.
[0026] In example embodiments, the second nitride semiconductor may
include a nitride that includes at least one of aluminum (Al),
gallium (Ga), indium (In) and boron (B).
[0027] In example embodiments, the depletion-forming layer may
include a p-type nitride semiconductor.
[0028] In example embodiments, the depletion-forming layer may
include a III-V group nitride semiconductor material.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] These and/or other aspects will become apparent and more
readily appreciated from the following description of non-limiting
example embodiments, taken in conjunction with the accompanying
drawings. The drawings are not necessarily to scale, emphasis
instead being placed upon illustrating principles of inventive
concepts.
[0030] FIG. 1 is a cross-sectional view schematically showing a
structure of a normally-off high electron mobility transistor
(HEMT) according to example embodiments;
[0031] FIG. 2 is a partial top view of the normally-off HEMT
according to example embodiments;
[0032] FIGS. 3A to 3C are cross-sectional views for describing an
operation of the normally-off HEMT according to example
embodiments;
[0033] FIG. 4 is a cross-sectional view schematically showing a
structure of a normally-off HEMT according to example
embodiments;
[0034] FIG. 5 is a cross-sectional view schematically showing a
structure of a normally-off HEMT according to example embodiments;
and
[0035] FIG. 6 is a top view showing an electrical connection
between a first gate electrode and a second gate electrode of FIG.
5.
DETAILED DESCRIPTION
[0036] Example embodiments will now be described more fully with
reference to the accompanying drawings, in which some example
embodiments are shown. Example embodiments, may, however, be
embodied in many different forms and should not be construed as
being limited to the embodiments set forth herein; rather, these
example embodiments are provided so that this disclosure will be
thorough and complete, and will fully convey the scope of example
embodiments to those of ordinary skill in the art. In the drawings,
the thicknesses of layers and regions are exaggerated for clarity.
Like reference numerals in the drawings denote like elements, and
thus their description may be omitted.
[0037] It will be understood that when an element is referred to as
being "connected" or "coupled" to another element, it can be
directly connected or coupled to the other element or intervening
elements may be present. In contrast, when an element is referred
to as being "directly connected" or "directly coupled" to another
element, there are no intervening elements present. As used herein
the term "and/or" includes any and all combinations of one or more
of the associated listed items. Other words used to describe the
relationship between elements or layers should be interpreted in a
like fashion (e.g., "between" versus "directly between," "adjacent"
versus "directly adjacent," "on" versus "directly on").
[0038] It will be understood that, although the terms "first",
"second", etc. may be used herein to describe various elements,
components, regions, layers and/or sections, these elements,
components, regions, layers and/or sections should not be limited
by these terms. These terms are only used to distinguish one
element, component, region, layer or section from another element,
component, region, layer or section. Thus, a first element,
component, region, layer or section discussed below could be termed
a second element, component, region, layer or section without
departing from the teachings of example embodiments.
[0039] Spatially relative terms, such as "beneath," "below,"
"lower," "above," "upper" and the like, may be used herein for ease
of description to describe one element or feature's relationship to
another element(s) or feature(s) as illustrated in the figures. It
will be understood that the spatially relative terms are intended
to encompass different orientations of the device in use or
operation in addition to the orientation depicted in the figures.
For example, if the device in the figures is turned over, elements
described as "below" or "beneath" other elements or features would
then be oriented "above" the other elements or features. Thus, the
exemplary term "below" can encompass both an orientation of above
and below. The device may be otherwise oriented (rotated 90 degrees
or at other orientations) and the spatially relative descriptors
used herein interpreted accordingly.
[0040] The terminology used herein is for the purpose of describing
particular embodiments only and is not intended to be limiting of
example embodiments. As used herein, the singular forms "a," "an"
and "the" are intended to include the plural forms as well, unless
the context clearly indicates otherwise. It will be further
understood that the terms "comprises", "comprising", "includes"
and/or "including," if used herein, specify the presence of stated
features, integers, steps, operations, elements and/or components,
but do not preclude the presence or addition of one or more other
features, integers, steps, operations, elements, components and/or
groups thereof. Expressions such as "at least one of," when
preceding a list of elements, modify the entire list of elements
and do not modify the individual elements of the list.
[0041] Example embodiments are described herein with reference to
cross-sectional illustrations that are schematic illustrations of
idealized embodiments (and intermediate structures) of example
embodiments. As such, variations from the shapes of the
illustrations as a result, for example, of manufacturing techniques
and/or tolerances, are to be expected. Thus, example embodiments
should not be construed as limited to the particular shapes of
regions illustrated herein but are to include deviations in shapes
that result, for example, from manufacturing. Thus, the regions
illustrated in the figures are schematic in nature and their shapes
are not intended to illustrate the actual shape of a region of a
device and are not intended to limit the scope of example
embodiments.
[0042] Unless otherwise defined, all terms (including technical and
scientific terms) used herein have the same meaning as commonly
understood by one of ordinary skill in the art to which example
embodiments belong. It will be further understood that terms, such
as those defined in commonly-used dictionaries, should be
interpreted as having a meaning that is consistent with their
meaning in the context of the relevant art and will not be
interpreted in an idealized or overly formal sense unless expressly
so defined herein.
[0043] FIG. 1 is a cross-sectional view schematically showing a
structure of a normally-off high electron mobility transistor
(HEMT) 100 according to example embodiments.
[0044] Referring to FIG. 1, a channel layer 120 is formed on a
substrate 110. The substrate 110 may be formed of, for example,
directed-bonded copper or a semiconductor material such as
sapphire, silicon (Si), silicon carbide (SiC), or gallium nitride
(GaN). However, this is only illustrative, and the substrate 110
may be formed of other various materials.
[0045] The channel layer 120 may be formed of a first nitride
semiconductor material. The first nitride semiconductor material
may be a group DI- V compound semiconductor material. For example,
the channel layer 120 may be a GaN group material layer. In detail,
the channel layer 120 may be a GaN layer. In this case, the channel
layer 120 may be an undoped GaN layer, and in some cases, the
channel layer 120 may be a GaN layer doped with desired (and/or
alternatively predetermined) impurities.
[0046] Although not shown, a buffer layer may be further provided
between the substrate 110 and the channel layer 120. The buffer
layer may reduce (and/or prevent) a decrease in crystallizability
of the channel layer 120 by alleviating a lattice constant
difference and a thermal expansion coefficient difference between
the substrate 110 and the channel layer 120. The buffer layer may
include a nitride including at least one among Al, Ga, In, and B
and may have a single-layer structure or a multi-layer structure.
For example, the buffer layer may be formed of AlN, GaN, AlGaN,
InGaN, AlInN, or AlGaInN. A seed layer (not shown) for growing the
buffer layer may be further provided between the substrate 110 and
the buffer layer.
[0047] A channel supply layer 130 may be formed on the channel
layer 120. The channel supply layer 130 may induce a
two-dimensional electron gas (2DEG) in the channel layer 120. The
2DEG may be formed in the channel layer 120 below the interface
between the channel layer 120 and the channel supply layer 130. The
channel supply layer 130 may be formed of a second nitride
semiconductor material that is different than the first nitride
semiconductor material forming the channel layer 120. The second
nitride semiconductor material may be different from the first
nitride semiconductor material with respect to at least one of a
polarization characteristic, an energy bandgap, and a lattice
constant. In detail, the second nitride semiconductor material may
be higher than the first nitride semiconductor material with
respect to at least one of the polarization rate and the energy
bandgap.
[0048] The channel supply layer 130 may be formed of at least one
nitride that includes at least one among Al, Ga, In, and B and may
have a single-layer structure or a multi-layer structure. In
detail, the channel supply layer 130 may be formed of at least one
of AlGaN, AlInN, InGaN, AlN, and AlGaInN. The channel supply layer
130 may be an undoped layer or a layer doped with desired (and/or
alternatively predetermined) impurities. The thickness of the
channel supply layer 130 may be, for example, less than several
tens of nm. For example, the thickness of the channel supply layer
130 may be equal to or less than about 50 nm, but the thickness is
not limited thereto.
[0049] A source electrode 161 and a drain electrode 162 may be
formed on the channel layer 120. For example, the source electrode
161 and drain electrode 162 may be formed at both sides of the
channel supply layer 130. The source electrode 161 and the drain
electrode 162 may be electrically connected to the 2DEG. As shown
in FIG. 1, the source electrode 161 and the drain electrode 162 may
be formed to be inserted inside the channel layer 120. However, the
configuration of the source electrode 161 and drain electrode 162
is not limited thereto. The source electrode 161 and the drain
electrode 162 may be variously formed. For example, the source
electrode 161 and the drain electrode 162 may be formed on the
channel supply layer 130.
[0050] A depletion-forming layer 140 may be formed on the channel
supply layer 130. The depletion-forming layer 140 includes a first
part 141 having a first thickness T1 and a second part 142 having a
second thickness T2 and a third part 143 having the second
thickness T2.
[0051] FIG. 2 is a partial top view of the normally-off HEMT 100
according to example embodiments. In FIG. 2, some components are
omitted for convenience of description.
[0052] Referring to FIG. 2, the first part 141 may have a strip
shape, and the second and third parts 142 and 143 may be formed
long at both sides of the first part 141 in a lengthy direction of
the first part 141. As shown in FIG. 2, the first part 141 may have
a first width W1, the second part 142 may have a second width W2,
and the third part 143 may have a third width W3. The first to
third widths W1 to W3 may be different from each other. For
example, the first width W1 may be greater than the third width W3
and the third width W3 may be greater than the second width W2.
However, example embodiments are not limited thereto, and the
depletion-forming layer 140 may be formed in various shapes. For
example, alternatively at least two of the first to third widths W1
to W3 may be equal.
[0053] The second part 142 may be formed to be spaced apart from
the source electrode 161 and the third part 143 may be formed to be
spaced apart from the drain electrode 162. The first part 141 may
be formed to be closer to the source electrode 161 than the drain
electrode 162. However, example embodiments are not limited
thereto.
[0054] The depletion-forming layer 140 may function to form a
depletion region in the 2DEG. An energy bandgap of a portion of the
channel supply layer 130, which is located below the
depletion-forming layer 140, may increase due to the
depletion-forming layer 140, resulting in forming the depletion
region of the 2DEG at a portion of the channel layer 120
corresponding to the depletion-forming layer 140. Thus, the 2DEG
may be cut off at a portion corresponding to the first part 141 of
the depletion-forming layer 140, and electron density of the 2DEG
may decrease at a portion corresponding to the second part 142 and
the third part 143 of the depletion-forming layer 140. Electron
densities of the 2DEG in a region between the depletion-forming
layer 140 and the source electrode 161 and a region between the
depletion-forming layer 140 and the drain electrode 162 are higher
than electron density of the 2DEG below the second part 142 and the
third part 143.
[0055] FIG. 1 shows that a region of the 2DEG having relatively
high electron density is discriminated from a region of the 2DEG
having relatively low electron density by the thicknesses of dots.
Electron density is high as dots are thick. A region in which the
2DEG is cut off may be a `cut-off region`, and the normally-off
HEMT 100 may have a normally-off characteristic due to the cut-off
region.
[0056] The depletion-forming layer 140 may include a p-type
semiconductor material. That is, the depletion-forming layer 140
may be a p-type semiconductor layer or a semiconductor layer doped
with p-type impurities. In addition, the depletion-forming layer
140 may be formed of a group DI- V nitride semiconductor.
[0057] For example, the depletion-forming layer 140 may be formed
of GaN, AlGaN, InN, AlInN, InGaN, or AlInGaN or doped with p-type
impurities such as magnesium (Mg). In detail, the depletion-forming
layer 140 may be a p-GaN layer or a p-AlGaN layer. The
depletion-forming layer 140 may cause an energy bandgap of a
portion of the channel supply layer 130 therebelow to increase,
thereby forming a cut-off region of the 2DEG or a region having
relatively low electron density.
[0058] An insulation layer 150 is formed on the depletion-forming
layer 140. The insulation layer 150 may be referred to as a gate
insulation layer 150 hereinafter. The gate insulation layer 150 may
be extended to cover the channel supply layer 130. The gate
insulation layer 150 may be formed to have the thickness of about
50 nm to about 300 nm. The gate insulation layer 150 may include at
least one among aluminum oxide (Al.sub.2O.sub.3), silicon oxide
(SiO.sub.x), silicon nitride (Si.sub.xN.sub.y), scandium oxide
(Sc.sub.2O.sub.3), aluminum nitride (AlN), gallium oxide
(Ga.sub.2O.sub.3), gadolinium oxide (Gd.sub.2O.sub.3), aluminum
gadolinium oxide (Al.sub.xGd.sub.2(.sub.1-x)O.sub.3), aluminum
gallium oxide (Al.sub.xGa.sub.2(1-x)O.sub.3), magnesium oxide
(MgO), and a combination thereof. Besides, any of insulation
materials used for typical transistors may be used as a material
for the gate insulation layer 150. An opening 152 is formed in the
gate insulation layer 150 to expose at least a portion of the
surface of the depletion-forming layer 140. For example, the
opening 152 may be formed on the upper surface of the first part
141 of the depletion-forming layer 140. The opening 152 may be a
through hole, a diameter of which is equal to or less than about
0.25 .mu.m.
[0059] A gate electrode 170 is formed on the gate insulation layer
150. The gate electrode 170 may be arranged above the
depletion-forming layer 140 and formed to contact the
depletion-forming layer 140 through the opening 152. The gate
electrode 170 may be formed to have a narrower area than the
depletion-forming layer 140 as shown in FIG. 2. Since a contact
area between the gate electrode 170 and the depletion-forming layer
140 is small (for example less than a width of the gate electrode
170), a leakage current is low and/or may be reduced. The gate
electrode 170 may include any of various metal materials and metal
compounds. The depletion-forming layer 140 may be formed to be
wider than a region of the gate electrode 170.
[0060] As shown in FIG. 1, although the depletion-forming layer 140
has two thicknesses in FIG. 1, example embodiments are not limited
thereto. For example, the depletion-forming layer 140 may have a
plurality of thicknesses, wherein a part having the thickest
thickness is formed at the central part or formed to be closer to
the source electrode 161 at the central part, and the remaining
parts have sequentially thinner thicknesses from the central
part.
[0061] FIGS. 3A to 3C are cross-sectional views for describing an
operation of the normally-off HEMT 100 according to example
embodiments. Hereinafter, a region of the 2DEG having relatively
high electron density is discriminated from a region of the 2DEG
having relatively low electron density by the thicknesses of dots.
Electron density is high as dots are thick.
[0062] An operation of the normally-off HEMT 100 according to
example embodiments will now be described with reference to FIGS. 1
and 3A to 3C.
[0063] FIG. 1 shows a normally-off state of the normally-off HEMT
100. A region below the first part 141 is a cut-off region D in
which the 2DEG does not exist.
[0064] Referring to FIG. 3A, when a voltage equal to or higher than
a threshold voltage is applied to the gate electrode 170, the 2DEG
is generated in a cut-off region D, thereby making the normally-off
HEMT 100 be in an ON state. That is, a channel formed below the
gate electrode 170 is in an ON state, and accordingly, a current
flows through the 2DEG formed in the channel layer 120. The
threshold voltage may vary according to the thickness of the first
part 141 of the depletion-forming layer 140 and doping density of
the first part 141.
[0065] Referring to FIG. 3B, when a voltage higher than a hole
injection voltage of the second part 142 and third part 143 of the
depletion-forming layer 140 is applied to the gate electrode 170,
holes are injected into the channel supply channel 130 from the
second part 142 and third part 143, and in response to the holes
injected into the 2DEG, electron density of the 2DEG in a region
below the depletion-forming layer 140 increases. Accordingly, an ON
resistance decreases.
[0066] Referring to FIG. 3C, when a voltage higher than a hole
injection voltage of the first part 141 of the depletion-forming
layer 140 is applied to the gate electrode 170, holes are injected
into the channel supply channel 130 from the first to third parts
141 to 143 of the depletion-forming layer 140, and in response to
the injected holes, electron density of the 2DEG in a region below
the depletion-forming layer 140 increases. Accordingly, the ON
resistance decreases further.
[0067] In the normally-off HEMT 100 according to example
embodiments, an area of the depletion-forming layer 140 below the
gate electrode 170 increases, resulting in expanding a gate region.
Since a contact area between the gate electrode 170 and the
depletion-forming layer 140 is small, a leakage current is low.
[0068] When a zero voltage is applied to the gate electrode 170, an
electric field is dispersed due to the first part 141 of the
depletion-forming layer 140 and the gate electrode 170, and
accordingly, a breakdown voltage of the normally-off HEMT 100
increases.
[0069] In addition, since the depletion-forming layer 140 is formed
to be apart from the source electrode 161, a leakage current path
connected from the gate electrode 170 to the source electrode 161
may be blocked.
[0070] FIG. 4 is a cross-sectional view schematically showing a
structure of a normally-off HEMT 200 according to example
embodiments. The same reference numerals are used for the same
(and/or substantially the same) components as those in the
normally-off HEMT 100 of FIG. 1, and their detailed description is
omitted.
[0071] Referring to FIG. 4, a depletion-forming layer 240 may be
formed on the channel supply layer 130. The depletion-forming layer
240 includes a first part 241 having the first thickness T1 and a
second part 242 having the second thickness T2, and a third part
243 having the second thickness T2. The first part 241 may have a
strip shape, and the second part 242 and third part 243 may be
formed long at both sides of the first part 241 in a lengthy
direction of the first part 241. However, example embodiments are
not limited thereto, and the depletion-forming layer 240 may be
formed in various shapes.
[0072] The second part 242 may be formed to contact the source
electrode 161 and the third part 243 may be formed to contact drain
electrode 162. The first part 241 may be formed to be closer to the
source electrode 161 than the drain electrode 162. However, example
embodiments are not limited thereto and the second part 242 and
third part 243 may be alternatively configured. For example, the
second part 242 may alternatively be formed similar to the second
part 142 in FIG. 1, which does not contact the source electrode
161. As another example, the third part 243 may alternatively be
formed similar to the third part 143 in FIG. 1, which does not
contact the drain electrode 162. In other words, in a HEMT
according to example embodiments, one of the second part 242 and
the third part 243 may alternatively be arranged so it does not
contact an adjacent one of the source electrode 161 and the drain
electrode 162.
[0073] The depletion-forming layer 240 may function to form a
depletion region in the 2DEG. An energy bandgap of a portion of the
channel supply layer 130, which is located below the
depletion-forming layer 240, may increase due to the
depletion-forming layer 240, resulting in forming the depletion
region of the 2DEG at a portion of the channel layer 120
corresponding to the depletion-forming layer 240. Thus, the 2DEG
may be cut off at a portion corresponding to the first part 241 of
the depletion-forming layer 240, and electron density of the 2DEG
may decrease at a portion corresponding to the second part 242 and
the third part 243 of the depletion-forming layer 240.
[0074] FIG. 4 shows that a region of the 2DEG having relatively
high electron density is discriminated from a region of the 2DEG
having relatively low electron density by the thicknesses of dots.
Electron density is high as dots are thick. A region in which the
2DEG is cut off may be a `cut-off region`, and the normally-off
HEMT 200 may have a normally-off characteristic due to the cut-off
region.
[0075] The depletion-forming layer 240 may include a p-type
semiconductor material. That is, the depletion-forming layer 240
may be a p-type semiconductor layer or a semiconductor layer doped
with p-type impurities. In addition, the depletion-forming layer
240 may be formed of a group III-V nitride semiconductor.
[0076] For example, the depletion-forming layer 240 may be formed
of GaN, AlGaN, InN, AlInN, InGaN, or AlInGaN or doped with p-type
impurities such as Mg. In detail, the depletion-forming layer 240
may be a p-GaN layer or a p-AlGaN layer. The depletion-forming
layer 240 may cause an energy bandgap of a portion of the channel
supply layer 130 therebelow to increase, thereby forming a cut-off
region of the 2DEG or a region having relatively low electron
density.
[0077] Since an etching process of both ends of the
depletion-forming layer 240 is unnecessary in the normally-off HEMT
200 according to example embodiments, a fabricating process of the
normally-off HEMT 200 may be simplified.
[0078] In addition, the expansion of the second part 242 and third
part 243 of the depletion-forming layer 240 may cause the ON
resistance to decrease further.
[0079] FIG. 5 is a cross-sectional view schematically showing a
structure of a normally-off HEMT 300 according to example
embodiments. The same reference numerals are used for substantially
the same components as those in the normally-off HEMT 100 of FIG.
1, and their detailed description is omitted.
[0080] Referring to FIG. 5, a depletion-forming layer 340 may be
formed on the channel supply layer 130. The depletion-forming layer
340 includes a first part 341 having the first thickness T1, a
second part 342 having the second thickness T2, and a third part
343 having the second thickness T2. The first part 341 may have a
strip shape, and the second part 342 and third part 343 may be
formed long at both sides of the first part 341 in a lengthy
direction of the first part 341. However, example embodiments are
not limited thereto, and the depletion-forming layer 340 may be
formed in various shapes.
[0081] The second part 342 may be formed to be apart from the
source electrode 161 and the third part 343 may be formed to be
apart from the drain electrode 162. However, example embodiments
are not limited thereto. The second part 342 may expand as in the
second part 242 of FIG. 4 and may be formed to contact the source
electrode 161 and the third part 343 may expand as in the third
part 243 in FIG. 4 and contact the drain electrode 162. The first
part 341 may be formed to be closer to the source electrode 161
than the drain electrode 162.
[0082] The depletion-forming layer 340 may function to form a
depletion region in the 2DEG. An energy bandgap of a portion of the
channel supply layer 130, which is located below the
depletion-forming layer 340, may increase due to the
depletion-forming layer 340, resulting in forming the depletion
region of the 2DEG at a portion of the channel layer 120
corresponding to the depletion-forming layer 340. Thus, the 2DEG
may be cut off at a portion corresponding to the first part 341 of
the depletion-forming layer 340, and electron density of the 2DEG
may decrease at a portion corresponding to the second part 342 and
the third part 343 of the depletion-forming layer 340.
[0083] FIG. 5 shows that a region of the 2DEG having relatively
high electron density is discriminated from a region of the 2DEG
having relatively low electron density by the thicknesses of dots.
Electron density is high as dots are thick. A region in which the
2DEG is cut off may be a `cut-off region`, and the normally-off
HEMT 300 may have a normally-off characteristic due to the cut-off
region.
[0084] The depletion-forming layer 340 may include a p-type
semiconductor material. That is, the depletion-forming layer 340
may be a p-type semiconductor layer or a semiconductor layer doped
with p-type impurities. In addition, the depletion-forming layer
340 may be formed of a group III-V nitride semiconductor. For
example, the depletion-forming layer 340 may be formed of GaN,
AlGaN, InN, AlInN, InGaN, or AlInGaN or doped with p-type
impurities such as Mg. In detail, the depletion-forming layer 340
may be a p-GaN layer or a p-AlGaN layer. The depletion-forming
layer 340 may cause an energy bandgap of a portion of the channel
supply layer 130 therebelow to increase, thereby forming a cut-off
region of the 2DEG or a region having relatively low electron
density.
[0085] A first gate electrode 371 is formed on the
depletion-forming layer 340. The first gate electrode 371 may be
formed mainly on the first part 341.
[0086] An insulation layer 350 may be formed on the first gate
electrode 371. The insulation layer 350 may be referred to a gate
insulation layer 350 hereinafter. The gate insulation layer 350 may
be formed to cover the depletion-forming layer 340 and the channel
supply layer 130. The gate insulation layer 350 may be formed to
have the thickness of about 50 nm to about 300 nm. The gate
insulation layer 350 may include at least one among
Al.sub.2O.sub.3, SiO.sub.x, Si.sub.xN.sub.y, Sc.sub.2O.sub.3, AlN,
Ga.sub.2O.sub.3, Gd.sub.2O.sub.3,
Al.sub.xGd.sub.2(.sub.1-x)O.sub.3,
Al.sub.xGa.sub.2(.sub.1-x)O.sub.3, MgO, and a combination thereof.
However, example embodiments are not limited thereto.
[0087] A second gate electrode 372 is formed on the gate insulation
layer 250. In detail, the second gate electrode 372 may be arranged
above the depletion-forming layer 340. The first gate electrode 371
and the second gate electrode 372 may be formed of any of various
metal materials and metal compounds. For example, the first gate
electrode 371 and the second gate electrode 372 may be formed of
titanium nitride (TiN), tungsten (W), platinum (Pt), or tungsten
nitride (WN) or formed in a multi-layer structure of
W/Ti/Al/Ti/TiN. The first gate electrode 371 may be formed to have
the thickness of about 100 nm to about 300 nm.
[0088] The first gate electrode 371 and the second gate electrode
372 may be electrically connected to each other by a wire 375.
[0089] FIG. 6 is a top view showing an electrical connection
between the first gate electrode 371 and the second gate electrode
372. For convenience of description, some components are not shown
in FIG. 6.
[0090] Referring to FIG. 6, the second gate electrode 372 is formed
on the first gate electrode 371, and the first gate electrode 371
is formed to be exposed by the second gate electrode 372. The wire
375 connects the exposed first gate electrode 371 to the second
gate electrode 372.
[0091] Although the first gate electrode 371 and the second gate
electrode 372 are connected to each other by the wire 375 in FIG.
6, example embodiments are not limited thereto. For example, the
second gate electrode 372 may be formed to directly contact the
exposed first gate electrode 371.
[0092] Alternatively, the first gate electrode 371 and the second
gate electrode 372 may be electrically connected to each other
through an opening (refer to 152 in FIG. 1) formed on the gate
insulation layer 350.
[0093] Although FIGS. 5-6 illustrate the depletion-forming layer
340 is spaced apart from the source 161 and drain electrodes 162,
example embodiments are not limited thereto. Alternatively, the
depletion-forming layer 340 of the HEMT 300 in FIGS. 5-6 may be
connected to at least one of the source 161 and drain electrodes
162.
[0094] Although FIGS. 5-6 illustrate the depletion forming layer
340 includes a second part 342 and a third part 343 that both have
the second thickness T2, example embodiments are not limited
thereto. For example, the second part 342 and the third part 343
may alternatively have different thicknesses.
[0095] Normally-off HEMTs according to example embodiments may
reduce (and/or prevent) a current from leaking in an OFF state and
may decrease a turn-on resistance. In addition, the expansion of a
depletion-forming layer causes an electric field to be dispersed,
and accordingly, a breakdown voltage of a normally-off HEMT
increases.
[0096] Example embodiments described herein should be considered in
a descriptive sense only and not for purposes of limitation.
Descriptions of features or aspects within each HEMT according to
example embodiments should typically be considered as available for
other similar features or aspects in other HEMTs according to
example embodiments. While some example embodiments have been
particularly shown and described, it will be understood by one of
ordinary skill in the art that variations in form and detail may be
made therein without departing from the spirit and scope of the
claims.
* * * * *